1. Field of the Invention
The present invention relates to a rotational angle detecting apparatus and, more particularly, to a rotational angle detecting apparatus coupled to a rotating member, such as an automotive-steering shaft, to cause two or more detection signals, which are based on the rotational angle and the rotational direction of a steering wheel, to be output so as to detect the rotational angle of the rotating member by employing the detection signals.
2. Description of the Related Art
In a conventional rotational angle detecting apparatus, a rotation detector employs a rotary sensor. As an example of the rotary sensor, the following rotary sensor will be described (this rotary sensor will be hereinafter referred to as xe2x80x9cthe conventional rotary sensorxe2x80x9d).
The proposed rotary sensor is constructed by a fixed base member, a rotor rotatable with respect to the base member, and a rotation detector that outputs a first sinusoidal detection signal and a second sinusoidal detection signal that are disposed between the base member and the rotor, and have a predetermined amplitude, the same cycle, and a phase difference of a quarter wavelength, and a third detection signal that maintains the same cycle over the whole rotational range of the rotor, and linearly increases in voltage value. During an operation, the rotor is coupled to a rotating member, e.g., an automotive steering shaft. In this case, the rotation detector is constituted by a first magnet and a second magnet disposed on the base member, a first Hall element and a second Hall element disposed such that they oppose the first magnet and are arranged with an angle of approximately 90 degrees, and a third Hall element disposed to oppose the second magnet, the three Hall elements being provided in the rotor.
In such a construction, when the steering wheel is turned to rotate the steering shaft connected thereto, the rotor coupled to the steering shaft rotates. This causes the rotation detector to generate the first detection signal, the second detection signal, and the third detection signal based on the rotational angle and the rotational direction of the steering shaft.
The first detection signal, the second detection signal, and the third detection signal that have been generated are supplied to a control unit mounted on a car. Based on the supplied third detection signal, the control unit detects a coarse rotational angle and the rotational direction of the steering wheel or the steering shaft from a neutral position. Based on the first detection signal and the second detection signal that have been supplied, the control unit further detects the fine rotational angle of the steering wheel or the steering shaft from the neutral position. The detected rotational angle and the rotational direction of the steering wheel or the steering shaft from the neutral position are supplied as detection information to a controller. Based on the supplied detection information, the controller decides on and detailedly carries out suspension control or traction control of the car.
FIG. 7 is a characteristic chart illustrating the relationship between the rotational angle of the steering wheel and the output voltages of the first detection signal, the second detection signal, and the third detection signal.
Referring to FIG. 7, reference numeral 71 denotes the first detection signal, reference numeral 72 denotes the second detection signal, and reference numeral 73 denotes the third detection signal. The chart illustrates the changes in the output voltages of the first through third detection signal 71 through 73 in the range of the rotational angle from 0 degrees to +225 degrees with respect to the rotational angle 0 degrees (neutral position) of the steering wheel.
In this case, the first detection signal 71 and the second detection signal 72 are composed of sine waves that share the same amplitude and the same cycle but are different in wavelength phase by a quarter. The voltage values of both the first detection signal 71 and the second detection signal 72 are 4.5 V at a maximum amplitude, and 0.5 V at a minimum amplitude. The first detection signal 71 reaches its minimum amplitude (voltage value: 0.5 V) at the rotational angles of +67.5 degrees and +157.5 degrees. The second detection signal 72 reaches its minimum amplitude (voltage value: 0.5 V) at the rotational angles of 0 degrees, +90.0 degrees, and +180.0 degrees. The voltage value of the third detection signal 73 linearly increases until the rotational angle reaches +225 degrees from zero degrees. The voltage value is 2.5 V when the rotational angle is zero degrees, and 3.0 V when the rotational angle is +180 degrees.
Referring to the characteristic chart shown in FIG. 7, the operation for detecting the rotational angle and the rotational direction of the steering wheel that is performed in the control unit will be described.
First, the control unit detects the direction in which the steering wheel is rotating with respect to the neutral position (rotational angle: 0 degrees) by means of the voltage value of the third detection signal 73 that has been supplied. More specifically, if the voltage value of the third detection signal 73 exceeds 2.5 V, then the control unit detects that the steering wheel is rotating in one direction, namely, the direction of a positive rotational angle. If the voltage value of the third detection signal 73 is below 2.5 V, then the control unit detects that the steering wheel is rotating in the other direction, namely, in the direction of a negative rotational angle.
Next, as shown in FIG. 7, the overall rotational angle of the steering wheel, e.g., 1440 degrees (xc2x1720 degrees), is divided into sections of angles (e.g. 90 degrees), each of which being equivalent to one wavelength of the first detection signal 71 and the second detection signal 72, . . . , Nxe2x88x921, N, N+1, . . . , thereby making it possible to detect, based on the voltage values of the supplied third detection signal 73, the coarse rotational angles that indicate the correspondence between the rotational angles of the steering wheel and the sections of angles. For example, if the control unit detects 2.8 V as the voltage value of the third detection signal 73, then an angle segment N is detected as the one that corresponds to the voltage value.
Subsequently, the control unit determines a first voltage value V1 and a second voltage value V2 at which the voltage values of the supplied first detection signal 71 and the second detection signal 72 agree in the detected angle segment N. The control unit then employs the determined first voltage value V1 and second voltage value V2 to identify one detection signal lying outside the range of the first voltage value V1 and the second voltage value V2 and the other detection signal lying within the range of the first voltage value V1 and the second voltage value V2.
The control unit then determines whether the other detection signal lying within the range of the first voltage value V1 and the second voltage value V2 is the first detection signal 71 or the second detection signal 72. At the same time, the control unit determines whether the one detection signal lying outside the range of the first voltage value V1 and the second voltage value V2 is smaller than the first voltage value V1 or larger than the second voltage value V2. The control unit further determines whether the other detection signal lying within the range of the first voltage V1 and the second voltage value V2 lies in a first divided angle segment H1, a second divided angle segment H2, a third divided angle segment H3, or a fourth divided angle segment H4 (angle segments H1 through H4 are formed by dividing the single angle section N into four segments). Thus, the fine rotational angle of the steering wheel is detected by determining in which of the divided angle segments H1 through H4 in the single angle segment N the other detection signal lies.
In this case, the other detection signal lying within the range of the first voltage value V1 and the second voltage value V2 will have the first angle segment H1 providing a linear rise (tilt or slope) portion 71U of the first detection signal 71, the second angle segment H2 providing a linear rise (tilt or slope) portion 72U of the second detection signal 72, the third angle segment H3 providing a linear fall (tilt or slope) portion 71D of the first detection signal 71, and the fourth angle segment H4 providing a linear fall (tilt or slope) portion 72D of the second detection signal 72.
In the rotational angle detecting apparatus having the conventional rotary sensor or the rotation detector set forth above, the first detection signal, the second detection signal, and the third detection signal are output from the rotation detector as the rotating member or the rotor rotates. To detect the rotational angle and the rotational direction of the rotating member on the basis of the supplied first through third detection signals, the control unit detects the rotational direction and the coarse rotational-angle of the rotating member on the basis of the amplitude or the voltage value of the third detection signal, and also detects the fine rotational angle of the rotating member on the basis of the linear slope portions of the first and second detection signals. Hence, the rotational direction and the rotational angle of the rotating member can be detected with high accuracy over a wide range.
However, in the rotational angle detecting apparatus equipped with the conventional rotary sensor or the rotation detector, the control unit uses the linear slope portions 71U, 71D, 72U, and 72D of the first and second detection signals in the first angle segment H1 through the fourth angle segment H4 to detect the fine rotational angle of the rotating member. Therefore, when the fine rotational angle to be detected is shifted from one angle segment (e.g. the first angle segment H1) to another angle segment (e.g. the second angle segment H2), the continuity of the amplitude between the preceding linear slope portion (e.g. 71U) and the following linear slope portion (e.g. 72U) breaks at the shifting point.
In general, if the preceding linear slope portion 71U and the following linear slope portion 72U do not include a rotational angle detection error, then the rotational angle detection value.based on the preceding linear slope portion 71U and the following linear slope portion 72U will not include an error.
However, the linear slope portions usually include small rotational angle detection errors, and the rotational angle detection values temporarily vary, depending on the error direction of the rotational angle detection errors, when shifting between the preceding linear slope portion 71U and the following linear slope portion 72U.
FIGS. 8A-8E are schematic representations showing the changes in the rotational angle detection values in relation to the changes in the amplitude of the linear slope portions, which are observed when a shift is made from one angle segment to another angle segment. The schematic representation illustrates cases where the error directions of the rotational angle detection errors in the linear slope portions are different.
Referring to FIG. 8A, when the fine rotational angle to be detected shifts from the first angle segment H1 to the second angle segment H2, and from the linear slope portion 71U to the linear slope portion 72U, if there is a rotational angle detection error of xe2x88x920.8% in the linear slope portion 71U and there is the same rotational angle detection error of xe2x88x920.8% in the linear slope portion 72U, as shown in FIG. 8B, or if there is a rotational angle detection error of +0.8% in the linear slope portion 71U and there is the same rotational angle detection error of +0.8% in the linear slope portion 72U, as shown in FIG. 8E, then the rotational angle detection values obtained when the shift from the linear tilt 71U to the linear tilt 720 takes place will be successive rotational angle detection values that include the same xe2x88x920.8% or +0.8%. Hence, the rotational angle detection values do not indicate temporary changes at shifts.
As shown in FIG. 8C, however, if the linear slope portion 71U includes a rotational angle detection error of xe2x88x920.8% and the linear slope portion 72U includes a rotational angle detection error of +0.8%, or the linear slope portion 71U includes a rotational angle detection error of +0.8% and the linear slope portion 72U includes a rotational angle detection error of xe2x88x920.8%, then the errors will be added to the rotational angle detection values when a shift from the linear slope portion 71U to the linear slope portion 72U takes place. As a result, at a shift, the rotational angle detection value will change (increase or decrease) by the rotational angle detection error of +1.6% or the rotational angle detection error of xe2x88x921.6%.
Thus, according to the rotational angle detecting apparatus having the conventional rotary sensor or rotation detector, when the control unit detects a fine rotational angle, a slight change may occur in a rotational angle detection value due to the rotational angle detection errors in the linear slope portions 71U, 71D, 72U, and 72D, causing the accuracy of the rotational angle detection to deteriorate accordingly.
The present invention has been made with a view toward solving the aforesaid problem, and it is an object of the present invention to provide a rotational angle detecting apparatus that reduces the influence of a rotational angle detection error included in a linear slope portion when detecting a fine rotational angle, thereby permitting highly accurate rotational angle detection to be accomplished.
To this end, according to one aspect of the present invention, there is provided a rotational angle detecting apparatus including a rotor connected to a rotating member, a rotation detector for successively detecting, as the rotor rotates, a first sinusoidal detection signal and a second sinusoidal detection signal that have a predetermined amplitude, the same cycle, and a phase difference of a quarter wavelength, a memory for storing the first detection signal and the second detection signal, and a control unit, wherein the control unit changes the weighting of the first detection signal and the second detection signal according to the area of the rotational angle of the rotating member when detecting a fine rotational angle of the rotating member on the basis of the amplitudes of the first detection signal and the second detection signal.
With this arrangement, when detecting the fine rotational angle of the rotating member on the basis of the amplitudes of the first detection signal and the second detection signal, weighting is imparted to the first detection signal and the second detection signal, and the weighting is changed according to the area of the rotational angle of the rotating member such that the weighting coefficient of a detection signal having a higher degree of linearity between the detection signals is set to be larger than the weighting coefficient of a detection signal having a lower degree of linearity. Hence, by selecting appropriate weighting coefficients and rotational angle areas, rotational angle detection values can be obtained with less influences of a rotational angle detection error even if a slight rotational angle detection error is included in the linear slope portion of one detection signal or the other detection signal. This permits a rotational angle detecting apparatus with high accuracy to be achieved.
Preferably, in the construction described above, the weighting of the first detection signal and the second detection signal is decided on the basis of three areas. The three areas include a first area within the range defined by one-sixth cycle preceding and following the point at which either the first detection signal or the second detection signal reaches its mid amplitude, a second area within the range of one-twelfth cycle of one detection signal lying outside the first area, and a third area within the range of one-twelfth cycle of one detection signal lying outside the second area. Preferably, the rotational angle of a rotating member is detected on the basis of the amplitude of one detection signal when one detection signal is present in the first area, the amplitude obtained by averaging the amplitude of one detection signal and the amplitude of the other detection signal at a ratio of 7 to 3 when one detection signal is present in the second area, and the amplitude obtained by averaging the amplitude of one detection signal and the amplitude of the other detection signal at a ratio of 5 to 5 when one detection signal is present in the third area.
With this arrangement, when the control unit detects a fine rotational angle by using the first detection signal and the second detection signal output from the rotation detector, the three areas, namely, the first area, the second area, and the third area, are defined for the cycle of one detection signal. Furthermore, depending on whether one detection signal lies in the first area, the second area, or the third area, the amplitude of one detection signal and the amplitude of the other detection signal are averaged at a predetermined ratio, preferably, 10 to 0, 7 to 3, or 5 to 5 so as to determine the fine rotational angle of the rotating member by employing the obtained average values. Hence, if the linear slope portion of one detection signal or the other detection signal includes a small rotational angle detection error, a rotational angle detection value can be obtained with less influences of the rotational angle detection error, thus enabling a rotational angle detecting apparatus with high accuracy to be achieved.
In a preferred form of the present invention, the rotating member is an automotive steering shaft, and the first detection signal and the second detection signal detect the steering angle of the steering shaft in cooperation with the third detection signal indicating the coarse rotational angle of the full rotation of the steering shaft.
With this arrangement, the rotational angle of an automotive steering shaft can be detected with high accuracy, permitting a power steering mechanism with high rotation control performance to be accomplished.
Preferably, a steering angle detection signal is supplied to a controller via a local area network bus line provided in a car.
With this arrangement, detection signals can be supplied to the controller without being affected by ambient noises or the like, so that malfunction of the controller can be prevented.